System of modulation utilizing a cathode follower



Patented Mar. 2, 1948 UNITED STATES T FFICE SYSTEM OF MODULATION UTILIZING A CATHODE FOLLOWER (Granted under the act of March 3, 1883, as amended April 30, 192.8; 370 0. G. 757) 4 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a system of modulation employing a cathode follower and which is suitable for use in signal generators and in low and moderate power transmitters.

A principal object of this invention is to provide a modulator utilizing a cathode follower which allows modulation at practically any frequency.

Another object is to provide such a modulator which has very little audio distortion.

These and other objects will become apparent in the specification and in the appended drawing in which Figures 1 and 2 illustrate schematically the circuit and arrangement of elements in the modulator.

In the drawing 9 and 10 are the terminals receiving the modulating voltage. A condenser II is in series between terminal 9 and the grid of a cathode follower tube [2. Between terminal l and the cathode of tube l2 are resistors l4l5 connected at their junction to resistor 13 to provide correct bias voltage. The cathode is further connected through radio frequency choke coil Hi to a radio frequency by-pass condenser I9 grounded as shown. The output end of choke i6 is connected to the tuned circuit comprising inductor l1 and variable condenser l8 which are in turn connected to the plate of tube 20, the latter elements comprising a modulated R. F. amplifier. The modulated R. F. output is taken from terminals 22 and 23 of coupled pickup coil 2|.

In operation, the cathode follower develops a D. C. voltage across resistors 14 and I5. This voltage is roughly half the B voltage applied to the cathode follower from the B voltage supply. This developed D. C. voltage is applied to the plate, screen, or other element or elements, of tube 20 to be modulated. In the example illustrated the voltage is applied to the plate of tube 20. When audio voltage is applied to the control grid of the cathode follower the developed D. C. voltage provided across I l-I varies at the audio rate and efiects modulation of the modulated R. F. amplifier. One of the advantages of the invention disclosed is that-it permits modumodulation may be corrected by adding a resistance 20!), Fig. 2, in series with choke It to lower the B voltage applied to the modulated R. F. amplifier, and bypassing the resistor to audio by means of a condenser 2 32. Other means for lowering the D. C. potential supplied to the modulated amplifier 20, may be utilized to increase the maximum degree of modulation possible.

Extremely 10W audio frequencies, even going to D. 0. input changes, may be used in the present invention by removing condenser il and by inserting a battery 204 for bias.

I claim:

1. A modulation circuit comprising a source of modulating signals, a first vacuum tube having an anode, a cathode, and at least one control electrode, said electrode being connected to said source, a cathode resistor grounding said cathode, a second vacuum tube having an anode, a cathode, and at least one control electrode, a source of carrier frequency connected to the control electrode of said second tube, and a coupling circuit between the plate of said second tube and said cathode resistor, whereby said resistor furnishes varying anode potential for said second tube for varying the amplitude of said carrier frequency in said coupling circuit.

2. A modulation circuit as defined in claim 1 in which said coupling circuit includes a tank circuit and a carrier frequency choke connected between said tank circuit and said resistor.

3. A modulation circuit as defined in claim 1 in which said coupling circuit includes a tank circuit and serially connected carrier frequency choke and a resistance shunted with a by-pass condenser, for connecting said tank circuit to said cathode resistor.

4. A modulator circuit as defined in claim 1 in which the connection between the electrode of said first tube and said source of modulating signals is a connection responsive to direct current.

JACK M. GLESSNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,233,317 Konkle Feb. 25, 1941 2,263,276 Pulley Nov. 18, 1941 

